1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an active matrix liquid crystal display device including color filters of red, green, and blue. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for reproducing images having near natural colors.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device includes two substrates that are spaced apart from and face into each other, and a liquid crystal material layer interposed between the two substrates. Each of the substrates includes electrodes that face into each other, wherein a voltage applied to each electrode induces an electric field between the electrodes. An alignment of liquid crystal molecules of the liquid crystal material layer, which has characteristics of dielectric anisotropy and spontaneous polarization, is changed by varying an intensity or direction of the applied electric field. Accordingly, the LCD device displays an image by varying light transmittance through the liquid crystal material layer in accordance with the arrangement of the liquid crystal molecules.
Recently, an LCD device, which includes pixels arranged in a matrix form and each pixel is controlled by a switching element, is widely used due to its high resolution and fast moving images. The LCD device is referred to as an active matrix LCD (AM-LCD) device, and a thin film transistor is generally used as the switching element.
Hereinafter, the liquid crystal display device according to the related art will be described with reference to FIG. 1.
FIG. 1 is an expanded perspective view of a liquid crystal display (LCD) device according to the related art. In FIG. 1, an LCD device 5 has first and second substrates 10 and 20, which are spaced apart from and facing into each other, and a liquid crystal layer 30 interposed between the first and second substrates 10 and 20.
A plurality of gate lines 13 and a plurality of data lines 15 are formed on the inner surface of the first substrate 10, whereby the gate lines 13 and the date lines 15 cross each other to define sub-pixel regions P having a matrix form, and a thin film transistor T is formed at each intersection of the gate lines 13 and the data line 15. The thin film transistor T is composed of a gate electrode, a source electrode, and a drain electrode. A pixel electrode 17, which is connected to the thin film transistor T, is formed in each sub-pixel region P. The liquid crystal layer 30 is applied with a voltage through the pixel electrode 17.
The second substrate 20 includes a black matrix 23, a color filter layer 25, and a common electrode 27 subsequently disposed on the inner surface thereof. The color filter layer 25 includes three sub-color filters of red (R) 25a, green (G) 25b, and blue (B) 25c alternating with one another. The black matrix 23 has openings such that each sub-color filter 25a, 25b, and 25c of the color filter layer 25 corresponds to the opening of the black matrix 23. The black matrix 23 corresponds to the gate lines 13, the data lines 15, and the thin film transistors T, exposing the pixel electrode 17 for displaying an image. The common electrode 27 is formed of a transparent conducting material and acts as another electrode for applying voltage to the liquid crystal layer 30.
Although not shown in the FIG. 1, a seal pattern is formed in the periphery between the first substrate 10 and the second substrate 20 in order to maintain a cell gap for injecting a liquid crystal material, to attach the substrates 10 and 20, and to prevent the liquid crystal material from leaking. A first alignment layer and a second alignment layer are formed between the first substrate 10 and the liquid crystal layer 30 and between the second substrate 20 and the liquid crystal layer 30, respectively.
In the liquid crystal display device, a common voltage Vcom is applied to the common electrode 27, a scanning voltage, which turns on or off the thin film transistor T, is applied to the gate line 13, and a data voltage (or an image voltage) is applied to the data line 15.
Therefore, when the thin film transistor T is turned on by the scanning voltage, the data voltage is provided to the pixel electrode 17 through the thin film transistor T. Liquid crystal molecules of the liquid crystal layer 30 are arranged according to the electric field induced between the common electrode 27 and the pixel electrode 17 by forming dipoles by a voltage difference between the common electrode 27 and the pixel electrode 17.
Optical modulation of the liquid crystal layer 30 occurs according to the arrangement of the liquid crystal molecules. Therefore, light transmittance of the liquid crystal material layer 30 in each sub-pixel can be controlled by transmitting or blocking light due to the optical modulation. In addition, color images of the LCD device are produced by mixing light that passes through red, green, and blue sub-color filters 25a, 25b, and 25c, each of which corresponds to each sub-pixel P. Therefore, a pixel, which functions as a basic unit for displaying an image, is composed of three sub-pixels.
There are visual cells in a retina of an eye, and the visual cells include three kinds of cone cells and rod cells. The cone cells distinguish colors of light and the rod cells distinguish light and shade. The cone cells are composed of L-cone cells that sense a red color, M-cone cells that perceive a green color, and S-cone cells that sense a blue color. Here, though there are differences among people, the S-cone cells are just 1/14 to 1/20 of other cone cells in number. Additionally, the three cone cells spread out all over the retina, and especially, are crowded in a fovea centralis. However, there exist no S-cone cells in the fovea centralis.
Thus, a distinguishable ability of blue color is deficient as compared to the other colors. If images are displayed in the LCD device having red, green, and blue sub-color filters, which are equal in number and size, intended images are different from the images shown by the LCD.
In order to solve the problem, a method increasing brightness of the blue sub-color filter may have been proposed, but this does not provide a complete solution. There is a limitation in that the LCD device displays images are different from the intended images.